We propose to develop, test, and apply a new computerized adaptive testing approach to measuring severity of depression, anxiety, mania, disruptive behavior, and attention-deficit/hyperactivity disorders in children and adolescents (9-17 years). This proposal contributes both methodologically and scientifically to research on the assessment of pediatric psychopathology. The proposed work will advance mental health research and improve psychiatric screening and monitoring in primary care. The methodological work proposed in this application is driven by a fundamental scientific challenge that has limited progress in measuring psychopathology in pediatric populations. We need to understand how the measurement of psychopathology in youth changes from childhood through adolescence. Our proposed work includes new statistical methodology for a Computerized Adaptive Test (CAT) based on multidimensional Item Response Theory (IRT) that allows us to tailor the measurement process to each child's developmental level (vertical scaling). The overarching aim of this application is to develop a CAT for children and adolescents that achieves the following goals: Aim 1: Provides dimensional severity scores for depression, mania, anxiety, disruptive behavioral disorders (DBDs), and attention-deficit/hyperactivity disorder (ADHD). Aim 2: Identifies children and adolescents who have symptom severity associated with functional impairment who would potentially benefit from a more extensive diagnostic assessment to evaluate the need for treatment. Aim 3: Uses differential item functioning to identify a set of items that optimally discriminate high and low levels of severity or each of psychopathology dimension equally well for parent and child ratings of that dimension. Aim 4:Accurately predicts DSM categorical diagnoses of major depressive disorder (MDD), ADHD, oppositional defiant disorder (ODD), conduct disorder (CD), anxiety disorders (AD; generalized anxiety disorder, separation anxiety disorder, social phobia, specific phobia), and bipolar disorder (BD). Exploratory Aim: Using the same powerful psychometric strategies, we will take several important steps toward developing and testing of a parallel CAT measure of two of the core biopsychological processes identified in the Research Domain Criteria (RDoC). To achieve these aims, we will develop a bank of approximately 1000 items addressing at different developmental levels symptoms of depression (including a subdomain of suicidality), mania, anxiety, DBDs and ADHD, as well as positive and negative valence RDoC domains. We will then calibrate the item bank using a bifactor IRT model and then develop, test and validate CAT-based administration.